Direct reduction process for making titanium

ABSTRACT

TITANIUM METAL IS RECOVERED FROM TITANIUM DIOXIDECONTAINING MATERIALS, SUCH AS RUTILE OR ILMENITE, BY REDUCTION OF THE ORE WITH A METALLIC REDUCING AGENT TO FORM AN ALLOY OF TITANIUM AND REFINING THE ALLOY TO RECOVER SUBSTANTIALLY PURE TITANIUM METAL.

United States Patent C 3,746,535 nmncr REDUCTION PROCES FOR MAKING TITANIUM Hans G. Brandstatter, Welland, Ontario, Canada, assignor to Ontario Research Foundation, Sheridan Park, Ontario, Canada Filed June 4, i971, Ser. No. 149,940 Claims priority, application Great Britain, June 8, 1970, 27,704/ 70 int. Cl. (12% 53/00 U.S. Cl. 75-845 16 Claims ABSTRACT OF THE DliSCLOS Titanium metal is recovered from titanium dioxidecontaining materials, such as rutile or ilmenite, by reduction of the ore with a metallic reducing agent to form an alloy of titanium and refining the alloy to recover substantially pure titanium metal.

This invention relates to the production of titanium, more particularly to the production of titanium from titanium dioxide-containing materials.

Titanium occurs naturally in the ores rutile, a crude form of titanium dioxide, and in ilmenite, a titaniferous ore of the approximate configuration FeQTiO containing varying amounts of haematite and/ or magnetite and gangue materials.

The only commercial process for the production of titanium metal is the so-called Kroll process which involves formation of titanium tetrachloride from titanium dioxidecontaining material such as rutile and benficiated ilmenite, followed by reduction of the tetrachloride with magnesium or sodium to titanium sponge. The process involves a large number of steps and hence the end product is somewhat expensive. Alternative processes have been investigated to provide a cheaper production method, none of which have been commercially acceptable.

Several proposals have been made to produce titanium by the reduction of titanium dioxide with reactive metals such as magnesium, calcium and aluminum. However, no commercial processes have been developed from these proposals mainly due to economic considerations.

The present invention provides a method of producing titanium by reduction of titanium dioxide-containing materials, such as pigmentary grade titanium dioxide, rutile, ilmenite and beneficiated ilmenite, i.e. ilmenite from which a substantial proportion of the iron oxide has been removed, which is competitive economically with the Kroll process.

The process of the invention involves reduction of a TiO -cQntaining material to form predominantly an alloy of titanium with the metallic reducing agent, and refining the alloy to recover substantially pure titanium metal.

It is preferred to use titanium dioxide-containing materials which are initially low in silicon, iron and vanadium, in view of the problems involved in removing these elements from the finished product as will become apparent hereinafter. When ilmenite is used as the source of titanium dioxide, it is preferred first to subject the ilmenite to beneficiation processes to remove a substantial proportion of the iron oxide from the ore.

Ilmenite may be beneficiated to remove substantial quantity of the iron oxides and gangue by a variety of ditferent processes known to the art.

It may be desired, after beneficiation of the ilmenite, to remove substantially completely the remaining iron oxides, such as by chlorination, typically using chlorine. The chlorination reaction is controlled so that while the iron oxides are converted to iron chlorides, titanium dioxide is substantially unaffected by the chlorination and 3,746,535 Patented July 17, 1973 only minimal amounts, if any, of titanium tetrachloride are formed.

In the first step, the titanium dioxide-containing material, such as beneficiated ilmenite, is reduced by a metallic reducing agent, generally aluminum or magnesium, in a thermite reaction to an alloy containing titanium as the major constituent, alloyed with excess reducing agent and minor amounts of reduced gangue materials, such as iron, silicon and chromium.

An excess of metallic reducing agent preferably is employed in order to ensure substantially complete reduction of the TiO to titanium metal.

The reduction reaction preferably is carried out in an inert atmosphere in order to minimize reoxidation of the titanium metal formed in the reduction. The inert atmosphere may be provided by any convenient inert gas, such as argon.

Any convenient form of reactor may be employed for the reduction process. Typically, the reaction may be carried out in a reactor employing magnesium oxide as refractory. Further, the reactor used for the reduction process may be an induction heated vessel. Conventional energy may be used to preheat, melt and superheat the metallic reducing agent and to preheat the TiO material. The balance of the energy requirement thereafter may be provided by the induction furnace.

The TiO material prior to reaction with the aluminum or other metallic reducing agent may be subjected to a reducing step, typically using carbon to reduce TiO to Ti O for example, at a temperature of from about 1500 to about 1600 C. This initial reduction with carbon reduces the quantity of metallic reducing agent which is required to achieve the ultimate reduction to titanium metal. It is not possible to reduce the TiO directly to titanium metal using carbon since the very stable titanium carbide is formed.

Alternatively, the TiO,, material may be subjected to a reducing reaction to convert the TiO,, to TiO, using carbon and an electric arc. As in the process outlined above, this initial reduction reduces the aluminum requirement to form the titanium. Some T iC also may be formed in this reducing step. As indicated above, TiC is a very stable material, resisting reduction to titanium metal and, therefore, reduction as far as TiO may be avoided.

Controlled quantities of flux may be added to the melt in the vessel to lower the bath temperature and thereby achieve higher titanium metal recoveries and lower residual aluminum levels.

The refining operation carried out on the alloy which is the product of the reaction involves a number of steps, including vacuum distillation, deoxidation, chlorination and remelting. The vacuum distillation removes the bulk of the unreacted metallic reducing agent and some silicon, chromium and iron. The metallic reducing agent removed is recovered and may be utilized again in the reduction of further TiO The vacuum distillation preferably is carried out in an induction-heated vessel employing CaO as the refractory material. The remaining atmosphere in the vessel after application of vacuum to the desired level preferably is constituted by an insert gas, such as argon gas. Temperatures of around 1600 to 1800 C. are satisfactory since at these temperatures, the formation of complex compounds between the metals present, such as TiAl, TiAl FeAl, FeAl FeAl FeTi, Fe Ti, FeSi and Fe Si is negligible and does not affect the partial pressure-temperature relationship between the metals present.

The vacuum distillation may be performed so that no titanium metal is removed. The materials remaining after this vacuum distillation still contains trace-amounts of the contaminating metals. More impurities may be re- 3 moved if the vacuum distillation is continued, but while such impurities are removed, some of the titanium also is removed.

The next step of the refining process involves deoxidation. This step is intended to reduce the residual oxygen content of the titanium, from several percentage points to approximately 0.3%. The residual oxygen mainly is present as an interstitial solution with titanium. Smaller amounts may be present as TiO, A1 and SiO;;.

The deoxidation preferably is achieved using calcium. The calcium may be added to the molten metal dissolved in calcium chloride or CaCh/CaF mixtures. The molten metal preferably is surrounded by an inert atmosphere, such as argon gas.

The molten bath preferably is stirred to promote reaction of the deoxidizing metal, generally calcium, with the titanium and other metal oxides. The products of the deoxidation reaction float to the surface of the bath and may be removed. It is preferred to hold the bath in a vessel utilizing a CaO refractory. The use of a CaO refractory in this and subsequent refining steps constitutes a novel feature of the invention.

Following this deoxidation, the titanium metal is further refined by subjecting the molten metal to chlorination, preferably with chlorine gas. Such chlorination constitutes a novel step in the refining of titanium metal.

The chlorination selectively forms chlorides of residual amounts of reducing metal, generally magnesium, or aluminum and of deoxidizing metal, such as calcium in preference to titanium, in view of the stronger afi'inity that these metals have for chlorine as compared to titanium. In this way, these impurity metals are readily removed as volatile materials. Small amounts of titanium may be lost in this step.

Any manganese present in the alloy also is removed in this step, but does not effectively remove any residual silicon, iron or vanadium. For this reason, it is preferable to commence with a TiO material low in these metals.

Alternatively, they may be substantially completely removed in the vacuum distillation step mentioned above, but, as indicated, such removal may involve losses of titanium metal.

The chlorination preferably is conducted on the molten metal contained in a vessel utilizing CaO as refractory and under an inert atmosphere, generally argon. Chlorine gas preferably is bubbled through the molten metal. The bath may have powdered lime floating on the surface. The chlorination may be conducted at temperatures of about 1600 to 1800 C.

A final deoxidation may be carried out, preferably with calcium. This final deoxidation with calcium preferably is carried out at the lowest possible temperature since it has been found that the effectiveness of calcium as a reducing agent for titanium oxides decreases with increasing temperature for the oz-SOllltiOIl range of TiO-solutions, increases with temperature in the a l- 8 phase solution range and then again decreases with increasing temperature in the B-solution range. A suitable temperature is about 900 C. yielding a residual oxygen content of approximately 0.02%

The steps of the refining operation described above all may be carried out in the same vessel or in separate vessels, as desired.

A final purification involves remelting under vacuum using, for example, a consumable electrode process or a hollow cathode beam melting technique.

The process of the present invention and a comparison with the conventional Kroll process are illustrated in the accompanying drawings, in which:

FIG. :1 is a flow diagram of one embodiment of the invention, and

FIG. 2 is a flow diagram of the prior art Kroll process.

Referring to FIG. 1, ilmenite, or any other convenient titanium dioxide material constituting the source of titanium, is fed by line 10 to a beneficiator 12. In those 4 cases where a non iron-containing ore is used in the formation of the titanium the beneficiation steps may be omitted.

In the beneficiator, a large majority of the iron oxides present in the ilmenite is removed and the titanium dioxide content of the ore concentrated. The iron oxides removed from the ilmenite are recovered by line 14.

The concentrated ore, still containing some iron oxides, is fed by line 16 to a chlorinator 18 which is operated under conditions to convert the remainder of the iron.

oxides to iron chlorides by chlorine fed by line 20 with minimum conversion of TiO to titanium tetrachloride. The iron chlorides, mainly FeCl are removed by line 22.

The iron oxides recovered by line 14 and the iron chlorides recovered by line 22 may be converted in any convenient manner to iron, or other iron compounds.

The product recovered from the chlorinator, crude TiO is fed by line 24 to a thermite reactor 26. In the thermite reactor, the TiO; is reacted with a metallic reducing agent, such as aluminum fed by line 28 to the thermite reactor 26. Flux may be fed by line 30 to aid in the reducing reaction. Recycled metal from a subsequent stage may be fed by line 32 to the reactor 26.

Slag is removed from the reactor 26 by line 34 and crude titanium metal, containing residual metallic impurities is fed to a refining vessel 36 by line 38, wherein the titanium is subjected to a plurality of refining operations.

Preferably, the refining vessel is constructed wholly of or has walls constructed of calcium oxide, although any other convenient material may be used.

An inert atmosphere, such as is provided by argon gas fed by line 40, is maintained throughout the refining operations or during only the deoxidation operation described below.

In the first refining operation, the crude titanium metal, in a molten state, is subjected to a vacuum distillation, which removes residual metallic reducing agent, which may be recycled by line 32 to the reactor 26. Also removed in the vacuum distillation are iron, silicon and chromium which are recovered by line 42.

The next refining operation involves deoxidation of the vacuum distilled titanium, typically using calcium fed by line 44 to the refiner 36. Following deoxidation, the titanium metal is subjected to chlorination, such as by chlorine gas fed by line 46, which forms chlorides of calcium and reducing metal, usually aluminum, and these chlorides are removed by line 48.

The purified titanium metal is passed by line 50 to a remelter 52 wherein the titanium metal is subjected to vacuum remelting and the ingot of titanium metal is recovered by line 54.

The process of the present invention, as illustrated by the above description in relation to FIG. 1, is much simpler and involves less steps than the conventional Kroll process which now will be described with reference to FIG. 2.

Ilmenite is fed by line to an acid leacher 112 wherein the ore is leached with hydorchloric acid fed by line 114. The leaching has the effect of removing a large proportion of the iron oxide present as iron chlorides, which are recovered from the leacher by line 116.

The resulting crude TiO is fed by line 118 to a chlorinator 118 by line 120. Chlorine is fed by line 122 to the chlorinator 118 which is operated under conditions to convert the TiO present to titanium tetrachloride. Under the operating conditions other metal compounds present in the crude Ti0 are converted to the corresponding metal chlorides and hence the gaseous titanium chloride formed in the chlorinator is contaminated with the other metal chlorides.

The crude titanium tetrachloride gas is passed by line 124 to a condenser 126 Where the gaseous materials are condensed to liquid and the crude titanium tetrachloride liquid is passed by line 128 to a fractional distillator 130.

The liquid is fractionally distilled and substantially pure titanium tetrachloride liquid is recovered overhead. The pure TiCl liquid passes from the distillator 130 by line 132 to a reactor 134 wherein the titanium tetrachloride reacts with magnesium metal fed by line 136 to form crude titanium sponge and magnesium chloride.

The magnesium chloride is removed from the reactor by line 138 and is passed by line 140 to an electrolysis cell 142. In the cell 142, the magnesium chloride is converted to magnesium which is recycled to the reactor 134 by line 136 and chlorine which is fed to the chlorinator 118 by line 122.

The crude titanium sponge is fed by line 144 to an acid leacher 146, fed by hydrochloric acid by line 148. The hydrochloric acid dissolves residual amounts of magnesium metal from the titanium and the magnesium chloride so formed is passed by line 150 to line 140.

The substantially pure titanium sponge formed in the leacher 146 still requires further processing to form titanium ingots. The sponge is passed by line 152 to a compactor 154 wherein the sponge is compacted to form an electrode, which then is passed by line 156 to a consuming electrode arc melter 158. The molten titanium is solidified and passed to a remelter 160 by line 162, from which ingots of titanium are recovered by line 164.

It will be seen from a comparison of the processes as described above with reference to FIGS. 1 and 2 that the process of the present invention involves fewer steps than the conventional Kroll process in the formation of titanium ingots. The process of the invention, therefore, is economically attractive in comparison to the Kroll process.

Many modifications are possible within the scope of the invention.

What I claim is:

1. A process for the production of titanium metal which comprises the sequential steps of:

reacting a titanium oxide-containing material with a stoichiometric excess of a metallic reducing agent capable of reducing titanium oxides to titanium metal to form an alloy containing titanium as the major constituent, excess metallic reducing agent and minor amounts of reduced gangue materials including silicon, chromium, iron and manganese;

vacuum distilling said alloy to remove the bulk of said excess metallic reducing agent and some of said silicon, chromium and iron while retaining substantially completely said titanium;

deoxidizing said alloy in the molten state with calcium metal to reduce the residual oxygen content of said titanium;

contacting the molten alloy with chlorine gas selectively to form chlorides of residual amounts of metallic reducing agent and said manganese;

cooling said chlorinated alloy;

remelting the cooled chlorinated alloy under vacuum;

and

cooling and recovering substantially pure titanium.

2. The process of claim 1 wherein said metallic reducing agent is aluminum or magnesium and the reducing action is a thermite process.

3. The process of claim 1 wherein said titanium oxidecontaining material is pigmentary grade titanium dioxide, rutile, ilmenite or beneficiated ilmenite.

4-. The process of claim 1 wherein said titanium oxidecontaining material is a titanium dioxide-containing material having low contents of silicon, iron and vanadium.

5. The process of claim 1 wherein said titanium oxidecontaining material is formed by reducing a titanium dioxide-containing material to Ti O or TiO.

6. The process of claim 1 wherein said deoxidation is continued to residual oxygen content in said titanium of about 0.3%.

7. The process of claim 1 wherein said calcium is dissolved in calcium chloride at CaCl /CaF mixtures.

8. Theprocess of claim 1 wherein said contact with chlorine gas is carried out in a vessel under an inert atmosphere at a temperature of about 1600 C. to 1800 C.

9. The process of claim 1 wherein said vacuum distillation is carried out in an induction heated vessel in an inert atmosphere at a temperature from about 1600 to 1800 C.

10. The process of claim 9 wherein said induction heated vessel has an inner wall of refractory material, said refractory material being C210.

'11. The process of claim 1 wherein said deoxidation is carried out in a vessel, the molten material is stirred in the vessel during said deoxidation, the products of deoxidation floating on the surface of the molten material are removed, and an inert atmosphere is maintained in contact with said molten material.

12. The process of claim 11 wherein said vessel has an inner wall of refractory material, said refractory material being CaO.

13. A process for the production of titanium metal which comprises the sequential steps of:

reacting a titanium oxide-containing material with a stoichiometric excess of a metallic reducing agent capable of reducing titanium oxides to titanium metal to form an alloy containing titanium as the major constituent, excess metallic reducing agent and minor amounts of reduced gangue materials including silicon, chromium, iron and manganese;

vacuum distilling said alloy to remove the bulk of said excess metallic reducing agent and some of said silicon, chromium and iron while retaining substantially completely said titanium;

deoxidizing said alloy in the molten state with calcium metal to reduce the residual oxygen content of said titanium;

contacting the molten alloy with chlorine gas selectively to form chlorides of residual amounts of metallic reducing agent and said manganese;

subjecting said chlorinated alloy to a further deoxidation step using calcium metal to reduce further the residual oxygen content of said titanium;

cooling the further deoxidized alloy;

remelting the cooled alloy under vacuum; and

cooling and recovering substantially pure titanium.

14. A process for the purification of a crude predominantly titanium metal-containing alloy formed by reduction of a titanium oxide-containing material with a metallic reducing agent capable of reducing titanium oxides to tit-anium metal, the crude alloy containing unreacted metallic reducing agent and reduced gangue materials, which comprises melting said alloy in a vessel, said vessel being formed with refractory walls of calcium oxide, subjecting the molten alloy to a plurality of purification steps while maintaining a substantially inert atmosphere in contact with said alloy, said plurality of steps including:

(a) vacuum distilling said alloy to remove the bulk of said unreacted metallic reducing agent and some silicon, chromium and iron;

(b) deoxidizing the alloy with calcium metal to reduce the residual oxygen content of said titanium; and

(c) contacting the alloy with chlorine gas selectively to form chlorides of residual amounts of metallic reducing agent and manganese;

cooling the chlorinated alloy, remelting the chlorinated alloy under vacuum, cooling and recovering substantially pure titanium.

15. A process for the removal of aluminum, magnesium and/or manganese impurities from titanium metal, which comprises contacting said impurities with chlorine gas to form volatile chlorides of said aluminum, magnesium and/ or manganese, removing said volatile chlorides and recovering titanium metal having a substantially reduced content of said impurities.

16. The process of claim 15 wherein said contact with 2,919,189 12/ 1959 Nossen et a1 75---84 chlorine gas is carried out in a vessel under an inert at- 2,834,667 5/1958 Rostron 7584 mosphere at a temperature of about 1600 to 1800 C. 2,807,539 9/1957 Quin 75-84 References Cited 5 CARL D. QUARFORTH, Primary Examiner UNITED STATES PATENTS B. HUNT, Assistant Examiner 3,627,508 12/1971 Hughes et a1. 75-112 3,240,557 3/1966 Lerner 7s 112 3,184,302 5/1965 Chindgren 7s-s4 75 849193E 

